Newer designs and manufacturing techniques have driven electronic components to small dimensions and miniaturized many communication devices and systems. Unfortunately, antennas have not been reduced in size at a comparative level and often are one of the larger components used in a smaller communications device. In those communication applications at below 6 GHz frequencies, the antennas become increasingly larger. In the 3 to 30 Mhz HF region for example, used by military, the proffered antennas become very large relative to operating platforms. A ¼ wave whip antenna for 5 Mhz is about 50 feet tall, and this is obviously unacceptable for use on a vehicle, and even fixed antennas require wire cage structures. It becomes increasingly important in these communication applications to reduce not only antenna size, but also to design and manufacture a reduced size antenna having a relatively broad gain bandwidth for a relatively small volume.
In current everyday communications devices, many different types of capacitor structures are used as antennas, which are the dipole antennas, the forms of which include the wire doublets, biconical dipoles, conical monopoles, discone antennas, and patch antennas. These are realized in a variety of different implementations. These antennas, however, are sometimes impractically large for the desired instantaneous bandwidth.
Conical antennas, which include a single inverted cone over a ground plane, and biconical antennas, which include a pair of cones oriented with their apexes pointing toward each other are used as broadband antennas for various applications, for example, direction finding. Referring to FIG. 1, a biconical antenna 10 includes a top inverted cone 12, a bottom cone 14 and a feed structure 16, as disclosed in U.S. Pat. No. 2,175,252 to Carter entitled “Short Wave Antenna”. An electronic coupler provides a connection to a feeding circuit that provides an electrical signal that feeds the antenna. The antenna is symmetric about the cone axis and each of the cones is a full cone, spanning 360°. Referring to FIG. 2, the antenna pattern beamwidth of a conventional biconical antenna is diagrammatically illustrated. As can be seen in the diagram, the beamwidth decreases as frequency increases. This may be undesirable for various applications.
Similarly, a single cone antenna includes a single antenna cone that also spans 360° and is symmetric about the cone axis. A single antenna cone is connected to an electronic coupler that provides a connection to a feeding circuit that provides an electrical signal to feed the antenna. The single cone antenna is located over a ground plane.
For example, U.S. Pat. No. 6,198,454 to Sharp et al. is directed to a broadband partial fan cone antenna. The antenna includes a radiator having a partial cone shape. U.S. Pat. No. 2,235,506 to Schelkunoff entitled “Ultra Short Wave Radio System”, describes the spheroidal and ellipsoidal geometries of single dipole doublets, having single resonant response. Multiple tuned responses, in which the antenna has a filter like polynomial response may be desirable in some applications.
Ultimately, there is a need for capacitive or dipole family antennas with greater instantaneous bandwidth, smaller size and stable beamwidth.